NLC Accelerator Physics

1
NLC Accelerator Physics

• Tor Raubenheimer
• SLAC DOE Review
• April 10, 2003

2
Introduction

• JLC/NLC Configuration
• US SC LC configuration
• Accelerator physics studies
• Sources
• Damping rings
• Beam delivery
• Integrated luminosity evaluation
• Damping ring -gt IP -gt dump dynamics studies
• Reliability / availability evaluation
• Vibration stabilzation studies

3
Beam Parameters

• Parameters also exist for operation at the
  Z, W, low-mass Higgs, and top

• Stage 2 has 5x1033 at 1.3 TeV

1300
25 Bunches
1200
CMS Energy (GeV)
Trade cms energyfor beam current
1100
192 Bunches
1000
0
0.5
1
1.5
2
2.5
3
Luminosity (1034)
4
JLC/NLC RF Configuration

• Baseline RF system has evolved significantly over
  the last year
• Moving towards a more conservative design to
  facilitate a technology comparison
• Will complete demonstration of the TRC R1
  (feasibility) items this year and should complete
  primary R2 item of demonstrating a full rf
  sub-unit by 2004
• Details of the RF configuration will be discussed
  by Chris, Sami, and David

5
Implications of New Baseline

• Changing the baseline rf pulse comp. system to
  SLED-II
• Faster demonstration of both power source and a
  full rf sub-unit, i.e. 1, 2, or 4 klystron pairs
  powering structures
• Depends on final modulator configuration
• Doubled number of klystrons, modulators, and PC
  systems and increased the linac length by 8
• Obvious cost impact perhaps some advantage in
  reliability
• Decrease in rf efficiency requires 8 additional
  linac AC power
• Decreased unloaded gradient by 7
• Reduced breakdown rate
• Tolerances scale with the square root of the
  gradient
• Changing from 90 cm to 60 cm HDS structures
• Faster demonstration of gradient and rf sub-unit
• Increases the number of klystrons, modulators,
  and PC systems by 10 (no change to linac length)

6
NLC Optical Configuration

• Optics has been relatively stable for last
• Improved damping ring designs for pre-damping
  ring and main damping ring
• Improved e yield from conventional source and
  further investigations of undulator-based
  polarized source
• Small changes to linac to follow rf configuration
  and tunnel schemes
• Use EM quads from better alignment control and
  flexibility
• Many small improvements to beam delivery system
  design
• Improvements to collimation system design
• Request that energy reach of Low Energy IR be
  at least 1.3 TeV
• Adoption of BNL-style SC final doublet magnets
• Further dump line studies to improve separation
  and diagnostics
• New baseline design will be documented in report
  due out in July

7
US Super-Conducting LC

• Many people from the NLC group are participating
  in the USLCSG comparison between a warm and cold
  LC in the US
• LC specifications from the ALCPG document
• Studies based on existing designs
• The warm version will be similar to the JLC/NLC
  design
• The cold version will be similar to the TESLA TDR
  design
• Four working groups (20 people)
• Accelerator design Gerry Dugan
• Site and conventional facilities Steve Holmes
• Cost and schedule David Burke
• Reliability/availability Tom Himel
• Complete comparison by September for the USLCSG

8
US SC LC

• TESLA TDR design was not entirely compatible with
  US specifications
• Changes to the TDR design
• Increase length to support 1 TeV at a maximum
  gradient of 35 MV/m without super-structures
• Use modified NLC BDS with crossing angle to avoid
  problems with head-on collisions
• Modify e source to operate at fixed energy and
  include operational overhead
• Use TESLA DR concept because we cannot do
  anything else
• Consider using two-tunnels for improved
  reliability / operability
• Possibly start with 35 MV/m for reduced cost and
  clearer comparison to X-band

9
LC Technical Review Committee
Two working groups (plus reliability)
Energy Technology Daniel Boussard
(Chair) Chris Adolphsen, SLACHans Braun,
CERN Yong-Ho Chin, KEK Helen Edwards, FNALKurt
Hubner, CERNLutz Lilje, DESY(Pavel Logatchov,
BINP)Ralph Pasquinelli, FNALMarc Ross,
SLAC(Tsumoru Shintake, KEK)Nobu Toge, KEKHans
Weise, DESYPerry Wilson, SLAC
Luminosity Gerald Dugan (Chair) Ralph Assmann,
CERNWinnie Decking, DESY Jacques Gareyte,
CERNWitold Kozanecki, SaclayKiyoshi Kubo,
KEKNan Phinney, SLACJoe Rogers, CornellDaniel
Schulte, CERNAndrei Seryi, SLACRon Settles,
MPIPeter Tenenbaum, SLACNick Walker, DESY Andy
Wolski, LBNL
10
TRC Energy Conclusions
JLC/NLC
TESLA
R1

• Test of complete accelerator structure at design
  gradient with detuning and damping, including
  study of breakdown and dark current
• Demonstration of SLED II pulse compression system
  at design power level
• Test of a complete main linac RF sub-unit (as
  identified in machine description) with beam
• Full test of KEK 75 MW, 1.6 µs PPM klystron at
  150 or 120 Hz
• Full test of SLAC induction mod.

• Building and testing of a cryomodule at 35 MV/m
  and measurement of dark current
• Test of a complete main linac RF sub-unit (as
  identified in machine description) with beam
• Testing of several cryomodules at nominal field
  (23.8 MV/m) over long enough periods to verify
  breakdown and quench rates, and measure dark
  current
• Test of RF components at higher powers for 800
  GeV operation

R1
R2
R2
R1 required for feasibility R2 required for
design
Deta
11
TRC Luminosity Conclusions
Common (JLC/NLC and TESLA)
TESLA Only

• Electron cloud and ion instabilities need study
• Additional simulations and experiments on e
  correction are needed for damping rings
• Demonstrate extraction kicker with better than
  0.1 stability
• Complete static DR?IP tuning simulations with
  dynamic effects
• Develop most critical beam instrumentation,
  including intra-train diagnostics
• Develop sufficiently detailed prototype of linac
  girder/cryostat to provide information on
  vibration

• Further optimization of damping ring dynamic
  aperture
• Study tighter alignment and electron cloud and
  ion instability requirements for 800 GeV upgrade
• Development of TESLA DR kicker
• Review trade-offs between head-on and
  crossing-angle collisions
• Detailed analysis of the tradeoffs between one
  and two-tunnel layouts
• Detailed evaluation of critical sub-system
  reliability

R2
R2
12
Positron Source Studies

• Continuing to study target limitations
• Improved yield in capture system for conventional
  source
• 30 now but still looking for an additional 30
  40
• Designing system for undulator-based source
• Fixed energy at 150 GeV location (keeps g energy
  at 10 MeV)
• Polarized e with yield of 1.4 requires 200 m
  helical undulator
• Total insert length is 900 meters with 2.5
  meter X separation
• We calculate yields 23 times lower than in TESLA
  TDR
• Conventional source is easier for TESLA than
  JLC/NLC

13
Damping Ring Studies

• New positron pre-damping ring with better dynamic
  aperture
• New main damping ring design with larger momentum
  compaction
• Eliminates single bunch instabilities from
  chamber impedance and CSR
• Reduces IBS to negligible levels
• Provides overhead on damping (could be run at 150
  Hz for JLC)
• Studying electron cloud impact on positron
  damping rings and positron beam lines
• Studying ion instability impact on electron
  damping ring and electron beam lines
• Work at ATF prototype ring at KEK studying
  beam-based alignment techniques

14
Why a new Damping Ring Design?

• Previous ring version dates from April 2001
• Driven by concern over nonlinear dynamics and
  radiation effects in the wiggler
• Minimized length of wiggler by using strong
  dipoles in the arcs (1.2 T)
• Momentum compaction was very small (0.310-3)
• Bunch length was very short (3.7 mm)
• Problems with collective effects
• CSR, IBS, µwave
• Further work suggested neither nonlinear dynamics
  nor collective radiation effects (CSR) in the
  wiggler limit the ring
• Developed a new lattice with longer wiggler (40m
  ? 60m)
• Increased momentum compaction by a factor of four
• Increased bunch length a factor of (nearly) two
• Reduce charge density, and raise thresholds for
  collective effects

15
Damping Ring Layout
Same circumference Longer wigglerSeparated
injection andextraction All the functionality
ofthe old ring with morecompact arc cells
wiggler
RF/ extraction
injection/ chicane
wiggler
16
Alignment Tolerances

• Compare random alignment and jitter tolerances
• Uncorrelated misalignments or jitter that would
  lead to equilibrium emittance, jitter equal to
  the beam size, or Dn 0.001
• These are not specs. on alignment but they are
  measures of the sensitivity
• Looking for significantly better alignment and
  stability than has been previously attained

17
ATF Beam-Based Alignment

• Have been testing beam-based alignment techniques
  at the ATF prototype damping ring
• Recently tested MIA tech-niques to correct
  dispersion
• First result looked good
• Second result looked notso good until sign flip
  was found!
• Vertical emittance wasreduced from 16 pm to10
  pm (gey 2.5e-8)
• Working on techniquesto correct the coupling

18
Electron Cloud Effects

• Neutralization density of electrons too high
• Single bunch instability 100 ms
• Multi-bunch instability 20 ms
• Investigating methods of reducing the electron
  density by three orders of magnitude

Studying e- cloud in the straights, bends,
quadrupoles, and wigglersStudying methods of
reducing thesecondary emission coefficient
19
Reduction of Secondary Emission

• Would like to reduce SEY to less than 1.4
• TiN coating but variation in results
• Surface treatments such as ion bombardment
• Test other promising materials or techniques
  (TiZrV, air baking, ...)
• Need better data on secondary electron spectrum
  and recombination rates
• LBL/SLAC collaborationconstructed a new
  facilityfor measuring SEY
• Compare with previous resultsand improve
  measurements
• Verify new techniques
• Many people interested in testingsamples

20
Beam Delivery System

• NLC beam delivery system is in good shape
• Starting detailed simulations of backgrounds and
  and diagnostic performance
• Simulations performed using MatLIAR, TURTLE,
  GEANT, and others
• New Raimondi/Seryi FFS design being adopted by
  all LCs
• More compact
• better bandwidth and nonlinear behavior
• Integrated collimation systemdesign is essential
  for luminosityoperation
• Collimation Task force verified NLC system

21
Integrated Luminosity

• Primary goal of beam dynamics studies!
• Huge problem to tackle
• The integrated luminosity consists of three
  parts
• Nominal (peak) luminosity
• Includes loss due to normal tuning fast
  feedbacks, beam jitter, static e dilutions
• Beam efficiency
• Includes trip recovery, invasive tuning time, and
  machine development
• Hardware availability
• Time lost due to inoperable hardware
• Approach from two sides
• Detailed studies of beam dynamics to get at the
  nominal luminosity
• Monte Carlo approach to study requirements on
  hardware with best estimates on recovery and
  tuning times

22
Low Emittance Transport

• LET simulations are performed using the MatLIAR
  code
• LIAR to simulate regions with accelerator
  structures wakefields
• Linear optics longitudinal position is fixed
• DIMAD to simulate bunch compressors and beam
  delivery system
• Many macro particles make this too slow for linac
  calculations
• GuineaPig to simulation beam-beam interaction
• MatLab drives the whole package allowing fast
  development of correction and feedback algorithms
• Package was compared against DESY and CERN codes
• Package has been used to
• Verify multibunch performance (not very
  interesting if done right)
• Study feedback system performance and effect of
  dynamic errors
• Study static alignment procedures
• Studies combining fast and slow effects are
  starting

23
Examples Dynamic studies
24
Examples Static Tuning
250 GeV linacplus bypass line Insensitive
toinitial alignment PM quads with25 mm errors
between quad and BPM centers (error arises
from BPMs with 0.4 mm resolution
25
Examples Static Tuning with Beam Jitter
Beam jitter rapidlydegrades alignmentalgorithm
effectiveness Main limitationis (probably) DFS
One motivation forreconsidering
EMquadrupoles 1600 vertical De/eafter
steering flatwill decreaseto about 50
26
Vibration and Stabilization

• Development ground motion models based on
  measurements from around the world
• Natural motion is not a limitation for operation
  (even case C, i.e. DESY site) but may limit the
  ability to tune
• Need to measure/model cultural sources
• Will likely be much more important than ground
  motion
• Presently assume 10 nm random (high frequency)
  vibration of most quadrupoles with 20 nm
  vibration of final doublet
• Working to quantify source of cultural noise
• Need to stabilize the final doublet in almost
  any scenario
• Demonstrated stabilization of rigid block
• Moving to stabilize and extended object

27
Cultural Noise Sources
NLCTA
Study of vibration of accelerating structures due
to RF pulse Cooling water

• Experiment shows that additional
  vibration of structures is acceptable
• Vibration coupling to linac quads is small.
  Design optimization is ongoing to make it
  negligible
• Vibration due to RF pulse is negligible

Acc.structure Quad mock-up
28
Cultural Noise Propagation
SLAC surface
Studied vibration transfer from surface to SLAC
tunnel Preparing to study vibration transfer
between parallel tunnels (using LA metro
lines) Made first studies of modulator vibration
signatures
SLAC tunnel
29
Final Doublet Stabilization
Study internal modes and stiffness in a
semi-realistic system
Springs Stages
3m magnet and 5.5m support have same
mechanical properties (mass, w) as final design
Assembly in Progress!
Support Cantilevered Beams
30
Compact Low Noise Sensors
beam
spring
upper electrode
mass
Lower electrode
picomotor
Two prototypes under test 10 planned
31
Summary

• JLC/NLC rf system is making great progress
• JLC/NLC is designed with an energy reach from 90
  GeV to 1.3 TeV
• NLC optical design is in good shape
• Luminosity issues are still a large concern
• Damping rings are essential for stable operation
• Lots of potential problems
• Both linear collider designs require complicated
  BBA procedures
• FFTB and SLC developed instrumentation and
  techniques necessary for beam-based alignment
  nobody can do a full demonstration
• Evaluation of integrated luminosity is very
  difficult
• Tools being developed to approach problem from
  two sides
• Either a SuperConducting or JLC/NLC collider
  could be built
• Different risks and different connections to the
  future
• Tools developed for JLC/NLC will be essential in
  either case